A smartwatch is a small computer you wear all day, so the right one depends on your phone, your habits and how often you are happy to charge it. Here is what to think about, in the order that usually matters.
Start with your phone
This is the first filter and the one people most often skip. Apple Watch works only with iPhone. Many other watches work with both Android and iPhone, but some features (replying to messages, certain apps, payments) may be limited or missing on one of the two. Watches made by a phone maker usually work best with that maker's phones. Before anything else, check the watch's compatibility page against your exact phone model and operating system version.
Health sensors: useful, not medical
Most watches today measure heart rate, blood oxygen (SpO2), sleep stages, steps and workouts. Some add skin temperature, stress estimates or an ECG function in certain countries. These readings are good for spotting trends: a resting heart rate drifting up over weeks, sleep getting shorter, activity dropping. They are not medical devices, and a single reading can be off because of fit, movement, skin tone or tattoos. If a watch shows something worrying, talk to a doctor rather than acting on the number alone, and never stop or change a medication because of a wearable.
Battery life trade-offs
Battery is the biggest compromise in this category. As a general pattern, full-featured watches with bright, app-rich displays last one to three days; simpler watches with lighter software last one to two weeks; and some sport watches with reflective screens last several weeks. Always-on display, GPS workouts, continuous SpO2 and very bright settings all cut battery noticeably. Decide honestly whether you will charge nightly. If not, favour longer-lasting models even if they do less.
Display types
AMOLED screens are vivid, with deep blacks and good indoor readability; they use more power when always on. LCD screens are cheaper and a bit dimmer. Memory-in-pixel (MIP) and e-paper screens look less flashy but are readable in direct sunlight and sip power, which is why outdoor watches use them. Check the peak brightness figure if you spend time outside in Egyptian sun.
Water resistance, explained
Watches use two different systems. ATM ratings (3 ATM, 5 ATM, 10 ATM) describe static pressure: 5 ATM is generally considered fine for swimming in a pool, while 3 ATM means splashes and rain only. IP ratings (for example IP68) describe dust and immersion in still fresh water for a limited time. Neither rating covers hot water, steam, soap, sea water over time or diving. If swimming matters, look for 5 ATM or better and a dedicated swim mode, and rinse the watch with fresh water after the sea or the pool.